Page 267 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

252 Chapter Three

where the same width of material is joined, weld tabs that extend
beyond the width of the joint would not be expected to carry signifi-
cant stress levels, making weld tab removal less important. Tab
removal from continuity plate welds is probably not justified.
The presence of weld tabs left-in-place is probably most significant for
beam-to-column connections where columns are box shapes. The natural
stress distribution under these conditions causes the ends of the groove
weld between the beam and column to be loaded to the greatest level,
the same region as would contain the weld tab. Just the opposite situation
exists when columns are composed of l-shaped members. The center of
the weld is loaded most severely, and the areas in which the weld tabs
would be located have the lowest stress level. For welds subject to high
levels of stress, however, weld tab removal is recommended.

Welds in combination with bolts. Welds provide a continuous metal-
lurgical path that relies upon the internal metallurgical structure of
the fused metal to provide continuity and strength. Mechanical fasten-
ers such as rivets and bolts rely on friction, shear of the fastening ele-
ment, or bearing of the joint material to provide for transfer of loads
between members. When welds are combined with bolts, caution must
be exercised in assigning load-carrying capacity to each joining method.
Traditionally it has been assumed that welds that are used in con-
junction with bolts should be designed to carry the full load, assuming
that the mechanical fasteners have no load-carrying capacity until the
weld fails. With the development of high-strength fasteners, it has been
assumed that loads can be shared equally between welds and fasten-
ers. This has led to connection details which employ both joining sys-
tems. In particular, the welded flange, bolted web detail used for many
beam-to-column connections in special moment-resisting frames
(SMRF) assumes that the bolted web is equally able to share loads with
the welded flanges. While most analysis suggests that vertical loads
are transferred through the shear tab connection (bolted) and moments
are transferred through the flanges (welded), the web does have some
moment capacity. Depending on the particular rolled shape involved,
the moment capacity of the web can be significant. Testing of speci-
mens with the welded web detail, as compared to the bolted web detail,
generally has yielded improved performance results. This has drawn
into question the adequacy of the assumption of high-strength bolts
sharing loads with welds when subject to inelastic loading. Research
performed after the Northridge earthquake provides further evidence
that the previously accepted assumptions may have been inadequate.
This is not to suggest that bolted connections cannot be used in con-
junction with welded connections. However, previous design rules
regarding the capacity of bolted connections need to be reexamined.
This may necessitate additional fasteners or larger sizes of shear tabs

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